Answer
$ \rho = 6 \times 10^2 \ kg/m^2$
Work Step by Step
We simplify the equation for flow speed in order to isolate density. Doing this, we obtain:
$ \rho = \frac{2\Delta P}{((\frac{A_1}{A_2})^2 - 1)v^2}$
We know that $\frac{A_1}{A_2}=4$. Plugging this in, the pressure as $16\times 10^3$, and the velocity as 1.9 meters per second, we obtain:
$ \rho = 6 \times 10^2 \ kg/m^2$
